Liquid crystal display element

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a liquid crystal display element and, more particularly, to the configuration of an additional capacitance region which is connected to its pixel electrodes.

[0002] Fig. 1 shows a conventional liquid crystal display element of a structure in which liquid crystal 14 is hermetically sealed in the space defined by a pair of opposed transparent substrates 11 and 12 as of glass with a spacer 13 interposed therebetween along their marginal edges. The one transparent substrate 11 has on its inside surface a plurality of pixel electrodes 15 each adjoined by a thin film transistor (hereinafter referred to as TFT) 16 serving as a switching element. The TFT 16 has its drain connected to the pixel electrode 15 corresponding thereto. The other transparent substrate 12 has on its inside surface a transparent common electrode 17 opposite the pixel electrodes 15.

[0003] As shown in Fig. 2, the pixel electrodes 15 substantially square in shape are closely arranged in rows and columns on the transparent substrate 11 and gate and source buses 18 and 19 extend adjacent and along the pixel electrodes 15 in the row and column directions, respectively. At each intersection of the gate and source buses 18 and 19 the TFT 16 is disposed, which has its gate connected to the gate bus 18, its source connected to the source bus 18 and its drain connected to the pixel electrode 15.

[0004] A voltage is applied across a pair of selected ones of the gate and source buses 18 and 19, the TFT 16 connected thereto at their intersection thus conducts to store charges in the pixel electrode 15 connected to the drain of the conducting TFT 16, and consequently, a voltage is applied across that portion of the liquid crystal 14 lying between the charged pixel electrode 15 and the common electrode 17 to make the liquid crystal 14 permit or inhibit the passage therethrough of light, thus providing a selective display. The display can be erased by discharging the charges stored in the pixel electrode 15.

[0005] Fig. 3 is an enlarged plan view showing one pixel and the neighboring portion in a conventional liquid crystal display element, Fig. 4 is a sectional view taken on the line IV-IV in Fig. 3, and Fig. 5 is a sectional view taken on the line V-V in Fig. 3. As shown in Figs. 3 and 4, the pixel electrode 15 and the source bus 19 of ITO or similar transparent conductive material are formed on the transparent substrate 11, a semiconductor layer 21 as of amorphous silicon is formed which bridges a gap between parallel, opposed marginal portions of the pixel electrode 15 and the source bus 19, and the pixel electrode 15, the source bus 19 and the semiconductor layer 21 are covered with a gate insulating film 22 as of silicon nitride. On the gate insulating film 22 a gate electrode 23 is formed which overlaps the pixel electrode 15 and the source bus 19 through the semiconductor layer 21. The gate electrode 23 is connected at one end to the gate bus 18. Thus, those portions of the pixel electrode 15 and the source bus 19 which are opposite to the gate electrode 23 form a drain electrode 15a and a source electrode 19a, respectively. The electrodes 15a and 19a, the semiconductor layer 21, the gate insulating film 22 and the gate electrode 23 constitute the TFT 16. The gate electrode 23 and the gate bus 18 are simultaneously formed using aluminum, for instance. A protective layer 23 for the liquid crystal is formed on the gate electrode 23 over the entire area of the display screen.

[0006] As depicted in Figs. 3 and 5, one marginal side portion of the pixel electrode 15 extends under the neighboring the gate bus 18 to substantially the center of the bus 18 widthwise thereof to form an additional capacitance region 30 between the extended portion 15b of the pixel electrode 15 and the gate bus 18. The additional capacitance region 30 is needed to supplement the electrostatic capacitance of the pixel electrode 15 to provide a large time constant composed of the electrostatic capacitance of the pixel electrode 15 and the resistance value of a channel region of the TFT 16.

[0007] The additional capacitance region 30 is composed of a plurality of divided capacitors. That is, the extended portion 15b of the pixel electrode 15 includes square electrodes 15b1, 15b2 and 15b3, each formed in the shape of an island under the gate bus 18 and connected to the pixel electrode 15 by a bridging segment 32. Electrostatic capacitances formed between the electrodes 15b1, 15b2 and 15b3 and the gate bus 18 are capacitors C₁ , C₂ and C₃ depicted in Fig. 2. If in the additional capacitance region a pinhole is made in or dust gets mixed into the gate insulating film 22 between the gate bus 18 and the underlying electrode 15b during manufacture, the insulation between the gate bus 18 and the electrode 15b may sometimes be impaired or shorting may develop therebetween. In such a case, some pixels in the display element always remain in the ON (lighted) state irrespective of an image signal to be displayed, resulting in the quality of the display being impaired. To avoid this, the defective additional capacitance region (i.e. defective one of the divided capacitors) is removed. That is, a focused laser beam is applied through the transparent substrate 12 in fig. 1 and is brought into a focus 2 to 10 »m in diameter on the bridging segment 32 coupled with the defective divided capacitor of the additional capacitance region 30 to cut the bridging segment 32 and hence cut the corresponding one of the electrodes 15b1, 15b2 and 15b3 off from the pixel electrode 15.

[0008] In the conventional liquid crystal display element, the removal of the defective divided capacitor of the additional capacitance region through laser cutting will reduce the capacitance value of the whole additional capacitance region to 2/3 its set value in the example of fig. 3. This will cause the potential of the pixel electrode relative to the common electrode to change from its set value, introducing a change in the brightness of the pixel. This does not pose a serious problem in the case of producing a simple black-and-white display, but in the case of providing a high-grade, multi-gradation display, the gradation of the pixel changes, impairing the quality of the display. The preamble of claim 1 reflects the above conventional element.

SUMMARY OF THE INVENTION

[0009] It is therefore an object of the present invention to provide a liquid crystal display element which permits repairing bad insulation of the additional capacitance region with practically no reduction in its capacitance.

[0010] Another object of the present invention is to provide a liquid crystal display element which is redesigned to prevent bad insulation of the additional capacitance region. According to the present invention, there is provided a liquid crystal display element comprising: a transparent substrate; a plurality of source buses and a plurality of gate buses formed on said transparent substrate at regular intervals in directions perpendicular to each other; thin film transistors, each including a drain electrode, a source electrode, a gate electrode, a semiconductor layer and a gate insulating film, and being connected to said source and gate buses at their intersection and formed at one corner in a mesh-like area defined by said source and gate buses; and pixel electrodes, each connected to the drain electrode of said thin film transistor and formed in said mesh-like area, said pixel electrode having an extended portion underlying said gate bus to form an additional capacitance region, the gate insulating film of said thin film transistor extending between said gate bus and said extended portion ; characterised in that a protective semiconductor layer covers said extended position of said pixel electrode, a reinforcing insulating film covers said protective semiconductor layer, and the gate insulating film of said thin film transistor is formed uniformly over said reinforcing insulating film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

Fig.1 is a sectional view showing a portion of a conventional liquid crystal display element;

Fig. 2 is an equivalent circuit diagram of the conventional liquid crystal display element;

Fig.3 is an enlarged plan view showing a pixel electrode and its vicinity of the conventional liquid crystal display element;

Fig. 4 is a sectional view taken on the line IV-IV in Fig. 3;

Fig. 5 is a sectional view taken on the line V-V in Fig. 3;

Fig. 6A is an enlarged plan view showing a part of an embodiment of the present invention;

Fig. 6B is a sectional view taken on the line VI-VI in Fig. 6A;

Fig. 7 is an electrical equivalent circuit diagram of the part surrounding a pixel electrode 15 in Fig. 6A;

Fig. 8A is a plan view for explaining how to repair an additional capacitance in Fig. 6A;

Fig. 8B is a sectional view taken on the line VIII-VIII in Fig. 8A;

Fig. 9A is an enlarged plan view illustrating the principal part of an embodiment of the present invention;

Fig. 9B is a sectional view taken on the line IX-IX in Fig. 9A;

Fig. 10A is a sectional view showing a manufacturing step of the liquid crystal display element of the Fig. 9A embodiment;

Fig. 10B is a sectional view showing another manufacturing step of the liquid crystal display element of the Fig. 9A embodiment;

Fig. 11 is an enlarged plan view illustrating the principal part of another embodiment of the present invention;

Figs. 12A and 12B are plan view showing an extended portion 15b and its vicinity for explaining the effect produced by a thin bridging segment 32; and

Fig. 13 is an enlarged plan view illustrating the principal part of still another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Referring now to Figs. 6A, 6B, 7, 8A and 8B, an embodiment of the present invention will be described. The parts corresponding to those in Figs. 1 through 5 are identified by the same reference numerals and no detailed description will be repeated with respect to them. In this embodiment, as shown in Figs. 6A and 6B, the bridging segment 32 of the comb-tooth-like electrode 15b1 has an islet 15c separated by a gap 40 from the pixel electrode 15. First and second electrodes 41 and 42 formed of a refractory metal (chromium, molybdenum, or the like) for laser welding use are provided on the islet 15c and the pixel electrode 15 facing each other across the gap 40. The refractory metal may be a well-known high-melting point material which is formed on the source bus for reducing its resistance value. The gate insulating film 22 is formed which covers the first and second electrodes 41 and 42 and fills the gap 40. A third electrode 43 for laser welding use is formed on the gate insulating film 22 in such a manner as to overlap the first and second electrodes 41 and 42 and the gap 40. The third electrode 43 is formed of the same material (aluminum, for instance) as that of the gate bus 18 and is patterned simultaneously with the gate bus 18.

[0013] A capacitor C_1a is formed between the comb-tooth-like electrode 15b1 and the gate bus 18. Capacitors C_1b and C_1c are formed between the first and third electrodes 41 and 43 and between the second and third electrodes 42 and 43, respectively. The three capacitors are connected in series as shown in Fig. 7. Utilizing the reference character of each capacitor for expressing its capacitance value, the following equation holds:


Assuming, for the sake of brevity, that


then,


As in the prior art structure, the capacitors C₂ and C₃ are formed between the comb-tooth-like electrodes 15b2 and 15b3 and the gate bus 18. Fig. 7 shows an equivalent circuit of one pixel electrode 15 and capacitances connected thereto.

[0014] The electrostatic capacitance values of the capacitors C₂ and C₃ and also set to C for the sake of simplicity.


Letting the whole additional capacitance value for the pixel electrode 15 be represented by C_T, it follows that

[0015] Where the capacitor C₃ is shorted, the bridging segment 32 of the comb-tooth-like electrode 15b3 is severed by laser cutting in the vicinity of the pixel electrode 15 as indicated by 44 in Fig. 8A. Then, a laser beam from a laser welder is applied through the transparent substrate 12 or 11 to the third electrode 43 and the center (indicated by a cross in Fig. 8A) of each of the first and second electrodes 41 and 24 underlying it, by which the first and second electrodes 41 and 42 are electrically connected by fused metal as indicated by 45 and 46 in Fig. 8B. As a result of this, the capacitors C_1b and C_1c are shorted to provide a composite capacitance C₁ = C_1a and the whole additional capacitance value becomes C_T′ = C + C_1a . It is necessary that the whole additional capacitance C_T′ = C + C_1a after repair be set to a value nearly equal to the whole additional capacitance C_T = C₁ + 2C in the normal state given by Eq. (5). That is,


On the other hand, when the capacitor C_1a is shorted, the comb-tooth-like electrode 15b1 is not severed but instead the additional capacitance value C_T˝ = C_1b/2 + 2C at that time must be set to a value substantially equal to the additional capacitance value C_T in the normal state. That is,


From Eq. (7) it follows that


From Eqs. (8) and (3) it follows that


To approximately satisfy Eq. (8) in practice, it is necessary only that


From Eq. (6) it follows that


Substitution of Eq. (8) into Eq. (6′) gives

[0016] To facilitate the understanding of the above, the invention will now be described more specifically. Setting C_1b = 0.5 pF, for example, it is necessary, from Eq. (9′) that C_1a >> 0.25 pF. Setting C = 1.0 pF in view of Eq. (10), then C_1a = 0.25 + 1.0 = 1.25 pF 1.2 pF; thus, Eq. (9′) can be satisfied by a rough approximation. Consequently, the capacitance C_1b, C and C_1a are set to 0.5, 1.0 and 1.2 pF, respectively. From Eq. (8) the composite capacitance C₁ = C_1b/2 = 0.25 pF, but since the capacitance value of each of the above-said capacitors is approximate, the capacitance C₁ may preferably be obtained accurately from Eq. (3); namely,


Further, the capacitance C_T,C_T′ and C_T˝ obtained from Eqs. (5), (6) and (7), respectively, are as follows:






It is seen from the above that the additional capacitance C_T′ after repair and the additional capacitance C_T˝ after shorting of the capacitor C_1a are both substantially equal to the normal additional capacitance C_T.

[0017] To sum up, when the capacitances C_1b and C_1c are selected small enough to satisfy the following condition in Fig. 7


the composite capacitance C₁ of these three capacitances is substantially C_1b/2 and this value is about the same, even if the capacitor C₁ is shorted. Hence, if the capacitance C_1a is selected substantially equal to the capacitance C₂ (=C₃) , then the total additional capacitance C_T in the case where none of the capacitors C_1a, C₂ and C₃ is defective is about 2C₂ (=2C₃) . Also in the case where either one of the capacitors C₂ and C₃, for example, the latter C₃ is shorted, the total additional capacitance C_T′ is made nearly equal to the sum of the capacitances C_1a and C₂ , i.e. 2C₂, by cutting off the capacitor C₃ through laser cutting and by shorting the capacitors C_1b and C_1c through laser welding.

[0018] While in the above the comb-tooth-like electrodes 15b1, 15b2 and 15b3 each have the narrow bridging segment 32 leading to the pixel electrode 15, the present invention is not limited specifically to the comb-tooth-like electrodes of such a configuration; for example, rectangular comb-tooth-like electrodes with no narrow portion may also be used. The first through third electrodes may also be shaped as desired. The number of comb-tooth-like electrodes need not always be three but needs only to be plural. Besides, it is also possible to provide a plurality of sets of electrodes similar to the set of electrodes 15b1, 41, 42 and 43.

[0019] As described above, in the case where either one of the divided additional capacitance regions C₂ or C₃ becomes of bad insulation, the bridging segment 32 of the defective capacitor is cut off by laser cutting, the first and second electrodes are electrically connected to the third electrode by laser welding and the additional capacitance C_1a established between the comb-tooth-like electrode 15b1 and the gate bus 18 is added, by which the additional capacitance value after repair can be made nearly equal to the normal additional capacitance value. Even if the additional capacitor C_1a shorts, the total additional capacitance value is held substantially equal to the normal value, and hence no adjustment of capacitance is needed. Hence, in either case mentioned above the brightness of the corresponding pixel hardly change, permitting an excellent multi-gradation display.

[0020] Although the above embodiment has been described to take steps to deal with shorting between the extended portion 15b of the pixel electrode 15 and the gate bus 18 in the additional capacitance region 30, it is also important to employ a structure in which such shorting is difficult to occur. Figs. 9A and 9B corresponding to Figs. 8A and 8B, respectively, show another embodiment in which the additional capacitance region 30 has a structure intended to prevent shorting. Figs. 10A and 10B are sectional views taken on the line X-X in Fig. 9A, showing the additional capacitance region 30 and its vicinity during manufacture. In the embodiment depicted in Figs. 9A and 9B a semiconductor layer 21 as of amorphous silicon for forming the TFT 16 is coated uniformly over the transparent substrate 11 on which there are deposited the pixel electrode 15, its extended portion 15b, the drain electrode 15a, the source bus 19 and the source electrode 19a, and then a reinforcing insulating film 31 as of silicon nitride is deposited on the semiconductor layer 21 (Fig. 10A). Then the additional capacitance region 30 and the semiconductor layer 21 and the reinforcing insulating film 31 of the TFT 16 are simultaneously patterned. Consequently, the TFT 16 also has the reinforcing insulating film 31 on the semiconductor layer 21. In this instance, the additional capacitance region 30 is patterned such that marginal portions of the semiconductor layer 21 and the reinforcing insulating film 31 protrude outwardly of the marginal edge of the extension 15b of the pixel electrode 15 to cover the electrodes 15b1, 15b2 and 15b3. Next, the gate insulating film 22 as of silicon nitride is formed uniformly over the substrate 11 and then the gate bus 18 and the gate electrode 23 of the TFT 16 are simultaneously formed on the gate insulating film 22 (Fig. 9B). As will be seen from Fig. 9B, the semiconductor layer 21, the reinforcing insulating film 31 and the gate insulating film 22 are sequentially formed between each of the electrodes 15b1, 15b2 and 15b3 and the gate bus 18 in the additional capacitance region 30, so that even if a pinhole is made in any one of the three layers, insulation is retained by the overlying or underlying layer. Unlike in the case of the conventional structure having only the gate insulating film 22, this embodiment is virtually free from the fear of bad insulation or shorting between the extended portion 15b of the pixel electrode 15 and the gate bus 18 owing to the influence of a pinhole or dust.

[0021] According to the embodiment shown in Figs. 9A and 9B, the probability of shorting or bad insulation per unit area in the additional capacitance region 30 is reduced, as referred to above. On the other hand, by maximizing the number of divided capacitors into which the additional capacitance region 30 is divided the change in the total capacitance by the separation of the defective one of the divided capacitors can be made acceptably small. In such a case, the electrodes 41, 42 and 43 for laser welding use shown in Fig. 9A need not be provided as depicted in Fig. 11, in which the parts corresponding to those in Fig. 9A are identified by the same reference numerals.

[0022] In the embodiment of Fig, 11 the additional capacitance region 30 is divided into four portions. The comb-tooth-like electrodes 15b1 through 15b4 of the extension 15b forming the respective additional capacitance regions are covered with an island-like common laminated structure composed of the semiconductor layer 21 and the reinforcing insulating film 31, and the electrodes are each connected to the pixel electrode 15 via the thin bar-shaped bridging segment 32.

[0023] With such a structure in which the additional capacitance region is divided into a plurality of portions as mentioned above, even if only a defective one of the divided capacitance portions is selectively cut off from the others, a decrease in the total additional capacitance can be made small within a given limit range, providing the operating margin of the TFT against a temperature change.

[0024] In the embodiment of Fig. 11, since the removal of a desired one of the divided capacitance portions can be accomplished simply by cutting the narrow bridging segment 32, the time therefore is short. Further, even if a patterning error occurs between the gate bus 18 and each extended portion 15b as depicted in Figs. 12A and 12B, their overlapping area hardly change, and hence the entire additional capacitance value undergoes substantially no change. The same results are also obtainable with the Fig. 8 embodiment. Fig. 12A shows the case where no patterning error is present between the gate bus 18 and the extended portion 15b and Fig. 12B shows the case where the gate bus 18 is shifted upwardly relative to the extended portion 15b. If the bridging segment 32 of each of the divided additional capacitance portions is not constricted in a narrow stripe form, the overlapping area of the divided extended portion 15b and the gate bus 18 in the case of Fig. 12B is appreciably small compared to the case in Fig. 12A, and hence the capacitance value is also small.

[0025] If the Fig. 11 embodiment can be made substantially free from defects such as shorting, by forming the semiconductor layer 21 and the reinforcing insulating film 31 between the extended portion 15b of each additional capacitance region 30 and the gate bus 18 as mentioned above, then the additional capacitance region 30 need not be divided. Fig. 13 illustrates an embodiment of such a structure. In this embodiment one marginal side portion of the pixel electrode 15 extends under the gate bus 18 to form the extended portion 15b, over which the semiconductor layer 21 and the reinforcing insulating film 31 are deposited in the shape of an island as in the case of Fig. 11, and they are covered with the gate insulating film 22 (see Fig. 9B)

[0026] Since the additional capacitance region 30 has, between the extended portion 15b and the gate bus 18, the three-layer structure composed of the semiconductor layer 21, the reinforcing insulating film 31 and the gate insulating film 21 as mentioned above, the possibility of bad insulation by a pinhole or dust can be reduced remarkably. With the structure in which the additional capacitance region is divided into a plurality of regions, when bad insulation occurs in any one of them, a decrease in the electrostatic capacitance can be suppressed by selectively cutting off the defective capacitance region.

[0027] With the structure in which each of the divided additional capacitance region 30 is formed in the shape of an island under the gate bus 18 its intermediate portion widthwise thereof and is connected to the pixel electrode 15 by the bridging segment 32, the time for laser cutting the defective capacitance region can be reduced markedly. Moreover, it is also possible to suppress a variation in the additional capacitance which is caused by a patterning error between the extended portion 15b and the gate bus 18.

[0028] It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

Claims

1. A liquid crystal display element comprising:
   a transparent substrate (11);
   a plurality of source buses (19) and a plurality of gate buses (18) formed on said transparent substrate at regular intervals in directions perpendicular to each other;
   thin film transistors (16), each including a drain electrode (15a), a source electrode (19a), a gate electrode (23), a semiconductor layer (21) and a gate insulating film (22), and being connected to said source and gate buses at their intersection and formed at one corner in a mesh-like area defined by said source and gate buses; and
   pixel electrodes (15), each connected to the drain electrode of said thin film transistor and formed in said mesh-like area, said pixel electrode having an extended portion underlying said gate bus to form an additional capacitance region, the gate insulating film of said thin film transistor extending between said gate bus and said extended portion ; characterised in that a protective semiconductor layer (21) covers said extended portion of said pixel electrode, a reinforcing insulating film (31) covers said protective semiconductor layer, and the gate insulating film (22) of said thin film transistor is formed uniformly over said reinforcing insulating film.

2. The liquid crystal display element of claim 1, wherein said extended portion of said pixel electrode is divided into a plurality of portions (15b1, 15b2, 15b3) to define divided additional capacitors.

3. The liquid crystal display element of claim 2, wherein each of said divided extended portions of said pixel electrode is formed in the shape of an island underlying said gate bus and is connected to said pixel electrode by a bar-shaped bridging segment (32).

4. A liquid crystal display element according to any preceding claim wherein
   the gate insulating film (22) is formed uniformly over said pixel electrode and its extended portion and in contact with the underside of said gate bus;
   wherein said extended portion of said pixel electrode is formed by a plurality of comb-tooth-like electrodes (15b);
   wherein at least one (15b1) of the said comb-tooth-like electrodes is separated by a gap (40) from said pixel electrode;
   wherein first and second electrodes (41, 42) for laser welding use are formed on said at least one comb-tooth-like electrode and said pixel electrode facing each other across said gap, said gate insulating film covering said first and second electrodes and filling said gap; and
   wherein a third electrode (43) for laser welding use is formed on said gate insulating film and overlaps said first and second electrodes and said gap, said third electrode defining first and second capacitances between it and said first and second electrodes.

5. The liquid crystal display element of claim 4, wherein each of said comb-tooth-like electrodes has a bridging segment (32) extending from its one end to said pixel electrode and narrower than said comb-tooth-like electrode body, said bridging segment extending from said at least one comb-tooth-like electrode having said first electrode (41) on its one end portion facing said pixel electrode across said gap, and said bridging segments of the other remaining comb-tooth-like electrodes are connected to said pixel electrode.

6. The liquid crystal display element of claim 4, wherein divided capacitors defined between said comb-tooth-like electrodes and said gate bus have about the same values, and said first and second capacitances have smaller values than said divided capacitors.

7. The liquid crystal display element of claim 4, wherein the protective semiconductor layer is formed between said comb-tooth-like electrodes and said gate bus, covering said comb-tooth-like electrodes, and the reinforcing insulating film formed on said protective semiconductor layer covers said comb-tooth-like electrodes.

8. The liquid crystal display element of claim 4, 5, 6, or 7 wherein said third electrode and said gate bus are patterned in the same step and are formed of the same metal.

Ansprüche

1. Flüssigkristall-Anzeigeelement, umfassend:
ein transparentes Substrat (11);
eine Vielzahl von Source-Bussen (19) und eine Vielzahl von Gate-Bussen (18), die auf dem transparenten Substrat in regelmäßigen Intervallen in Richtungen senkrecht zueinander gebildet sind;
Dünnfilmtransistoren (16), die jeweils eine Drain-Elektrode (15a), eine Source-Elektrode (19a), eine Gate-Elektrode (23), eine Halbleiterschicht (21) und einen Gate-Isolationsfilm (22) umfassen und mit den Source- und Gate-Bussen an deren Schnittpunkt verbunden und an einer Ecke in einem durch die Source- und Gate-Busse definierten gitterartigen Bereich gebildet sind; und
Pixelelektroden (15), die jeweils mit der Drain-Elektrode des Dünnfilmtransistors verbunden und in dem gitterartigen Bereich gebildet sind, wobei die Pixelelektrode einen verlängerten Abschnitt aufweist, der unter dem Gate-Bus liegt, um einen zusätzlichen Kapazitätsbereich zu bilden, wobei sich der Gate-Isolationsfilm des Dünnfilmtransistors zwischen dem Gate-Bus und dem verlängerten Abschnitt erstreckt;
dadurch gekennzeichnet, daß eine schützende Halbleiterschicht (21) den verlängerten Abschnitt der Pixelelektrode abdeckt, ein Verstärkungs-Isolationsfilm (31) die schützende Halbleiterschicht abdeckt und der Gate-Isolationsfilm (22) des Dünnfilmtransistors gleichmäßig über dem Verstärkungs-Isolationsfilm gebildet ist.

2. Flüssigkristall-Anzeigeelement nach Anspruch 1, dadurch gekennzeichnet, daß der verlängerte Abschnitt der Pixelelektrode in eine Vielzahl von Abschnitten (15b1, 15b2, 15b3) aufgeteilt ist, um aufgeteilte zusätzliche Kapazitäten zu definieren.

3. Flüssigkristall-Anzeigeelement nach Anspruch 2, dadurch gekennzeichnet, daß jeder der aufgeteilten verlängerten Abschnitte der Pixelelektrode in der Form einer unter dem Gate-Bus liegenden Insel gebildet und mit der Pixelelektrode durch ein stabförmiges Überbrückungssegment (32) verbunden ist.

4. Flüssigkristall-Anzeigeelement nach einem der vorangehenden Ansprüche,
dadurch gekennzeichnet, daß
der Gate-Isolationsfilm (22) gleichförmig über der Pixelelektrode und ihrem verlängerten Abschnitt und in Kontakt mit der Unterseite dse Gate-Busses gebildet ist; wobei der verlängerte Abschnitt der Pixelelektrode durch eine Vielzahl von kammzinkenartigen Elektroden (15b) gebildet ist;
wobei wenigstens eine (15b1) der kammzinkenartigen Elektroden von der Pixelelektrode durch einen Spalt (40) getrennt ist;
wobei erste und zweite Elektroden (41, 42) für eine Laserschweißverwendung auf der wenigstens einen kammzinkenartigen Elektrode und der Pixelelektrode, die einander an dem Spalt gegenüberliegen, gebildet sind, wobei der Gate-Isolationsfilm die ersten und zweiten Elektroden abdeckt und den Spalt ausfüllt; und
wobei eine dritte Elektrode (43) für eine Laserschweißverwendung auf dem Gate-Isolationsfilm gebildet ist, und die ersten und zweiten Elektroden und den Spalt überlappt, wobei die dritte Elektrode erste und zweite Kapazitäten zwischen ihr und den ersten und zweiten Elektroden definiert.

5. Flüssigkristall-Anzeigeelement nach Anspruch 4, dadurch gekennzeichnet, daß jede der kammzinkenartigen Elektroden ein Überbrückungssegment (32) aufweist, welches sich von ihrem einen Ende zu der Pixelelektrode erstreckt und schmaler als der kammzinkenartige Elektrodenkörper ist, wobei sich das Überbrückungssegment von der wenigstens einen kammzinkenartigen Elektrode erstreckt, die die erste Elektrode (41) auf ihrem einen Endabschnitt gegenüberliegend der Pixelelektrode an dem Spalt aufweist, und wobei die Überbrückungssegmente der anderen übrigen kammzinkenartigen Elektroden mit der Pixelelektrode verbunden sind.

6. Flüssigkristall-Anzeigeelement nach Anspruch 4, dadurch gekennzeichnet, daß aufgeteilte Kondensatoren, die zwischen den kammzinkenartigen Elektroden und dem Gate-Bus definiert sind, ungefähr die gleichen Werte aufweisen, und die ersten und zweiten Kapazitäten kleinere Werte als die aufgeteilten Kondensatoren aufweisen.

7. Flüssigkristall-Anzeigeelement nach Anspruch 4, dadurch gekennzeichnet, daß die schützende Halbleiterschicht zwischen den kammzinkenartigen Elektroden und dem Gate-Bus gebildet ist, abdeckendi er die kammzinkenartigen Elektroden, und der auf der schützenden Halbleiterschicht gebildete Verstärkungs-Isolationsfilm die kammzinkenartigen Elektroden überdeckt.

8. Flüssigkristall-Anzeigeelement nach Anspruch 4, 5, 6 oder 7,
dadurch gekennzeichnet, daß die dritte Elektrode und der Gate-Bus in dem gleichen Schritt strukturiert werden und aus dem gleichen Metall gebildet sind.

Revendications

1. Elément d'affichage à cristaux liquides, comprenant :
   un substrat transparent (11) ;
   plusieurs bus de sources (19) et plusieurs bus de grilles (18) formés sur ledit substrat transparent à des intervalles réguliers dans des directions perpendiculaires les unes aux autres ;
   des transistors à couches minces (16), chacun comprenant une électrode de drain (15a), une électrode de source (19a), une électrode de grille (23), une couche semi-conductrice (21) et un film d'isolation de grille (22), et étant connectés auxdits bus de sources et de grilles au droit de leurs intersections et étant formés au droit d'un coin d'une zone en forme de treillis définie par lesdits bus de sources et de grilles ; et
   des électrodes de pixel (15), chacune connectée à l'électrode de drain dudit transistor à couche mince et formées dans ladite zone en forme de treillis, ladite électrode de pixel ayant une partie prolongée se trouvant sous ledit bus de grilles pour former une région de capacité additionnelle, le film d'isolation de grille dudit transistor à couches minces s'étendant entre ledit bus de grilles et ladite partie prolongée ; caractérisé en ce qu'une couche semi-conductrice de protection (21) recouvre ladite partie prolongée de ladite électrode de pixel, en ce qu'un film isolant de renfort (31) recouvre ladite couche semi-conductrice de protection, et en ce que le film d'isolation de grille (22) dudit transistor à couches minces est formé de façon uniforme sur ledit film isolant de renfort.

2. Elément d'affichage à cristaux liquides selon la revendication 1, dans lequel ladite partie prolongée de ladite électrode de pixel est divisée en plusieurs parties (15b1, 15b2, 15b3) pour définir des capacités additionnelles élémentaires.

3. Elément d'affichage à cristaux liquides selon la revendication 2, dans lequel chacune desdites parties prolongées élémentaires de ladite électrode de pixel est conformée à la forme d'un îlot se trouvant sous ledit bus de grilles et est connecté à ladite électrode de pixel par un segment formant pont en forme de barre (32).

4. Elément d'affichage à cristaux liquides selon l'une quelconque des revendications précédentes,
   dans lequel le film d'isolation de grille (22) est formé uniformément sur ladite électrode de pixel et sa partie prolongée et en contact avec le côté inférieur dudit bus de grilles ;
   dans lequel ladite partie prolongée de ladite électrode de pixel est formée de plusieurs électrodes en forme de dent de peigne (15b) ;
   dans lequel au moins l'une (15b1) desdites électrodes en forme de dent de peigne est séparée par un espace (40) de ladite électrode de pixel ;
   dans lequel des première et seconde électrodes (41, 42) destinées à être soudées au laser sont formées sur ladite au moins une électrode en forme de dent de peigne et ladite électrode de pixel qui sont en face l'une de l'autre de chaque côté dudit espace, ledit film d'isolation de grille recouvrant lesdites première et seconde électrodes et remplissant ledit espace ; et dans lequel une troisième électrode (43) destinées à être soudée au laser est formée sur ledit film d'isolation de grille et recouvre partiellement lesdites première et seconde électrodes et ledit espace, ladite troisième électrode définissant des première et seconde capacité entre elle et lesdites première et seconde électrodes.

5. Elément d'affichage à cristaux liquides selon la revendication 4, dans lequel chacune desdites électrodes en forme de dent de peigne comporte un segment formant pont (32) s'étendant depuis sa première extrémité vers ladite électrode de pixel et qui est plus étroit que ledit corps d'électrode en forme de dent de peigne, ledit segment formant pont s'étendant de ladite au moins une électrode en forme de dent de peigne portant ladite première électrode (41) sur sa première partie d'extrémité qui fait face à ladite électrode de pixel de chaque côté dudit espace, et lesdits segments formant pont des autres électrodes en forme de dent de peigne restantes sont connectés à ladite électrode de pixel.

6. Elément d'affichage à cristaux liquides selon la revendication 4, dans lequel des condensateurs élémentaires définis entre lesdites électrodes en forme de dent de peigne et ledit bus de grilles ont à peu près les mêmes valeurs, et dans lequel lesdites première et seconde capacités ont des valeurs plus petites que lesdits condensateurs élémentaires.

7. Elément d'affichage à cristaux liquides selon la revendication 4, dans lequel la couche semiconductrice de protection est formée entre lesdites électrodes en forme de dent de peigne et ledit bus de grilles, en recouvrant lesdites électrodes en forme de dent de peigne, et dans lequel le film isolant de renfort formé sur ladite couche semi-conductrice de protection recouvre lesdites électrodes en fornie de dent de peigne.

8. Elément d'affichage à cristaux liquides selon la revendication 4, 5, 6 ou 7, dans lequel ladite troisième électrode et ledit bus de grilles sont dessinés au cours de la même étape et sont faits du même métal.

Drawing